Some X-ray image diagnosis apparatuses have the Automatic Brightness Control System (hereinafter, abbreviated as “ABS”) that automatically controls a tube voltage so that brightness of a fluoroscopic image is always constant even if an object thickness is changed. As an example of the control method, there is a method where a region of interest is set for an image region output from an X-ray detector; an average brightness value in the region of interest is used as a feedback signal; and a tube voltage is automatically controlled so that a feedback signal value nears a target brightness value set in advance. Then, when the feedback signal is lower than the target brightness value, X-ray output increases by the tube voltage working in a rising direction, and the brightness of the next fluoroscopic image is controlled so that it is brighter than that before rising.
Patent Literature 1 discloses a fluoroscopic imaging apparatus that can set a region of interest with a pointing device such as a mouse during X-ray fluoroscopic imaging and performs feedback for ABS using image data in the region of interest as an example of the ABS control.